Conventionally, etalons have been used in optical equipments such as optical communication equipments, measuring equipments, semiconductor lasers.
These etalons include solid types that are formed into cube shapes and air gap types that are configured by bonding ring-shaped members between transparent components which form parallel plates.
These etalons are provided in the paths for passage of light in optical equipment and are used while aligning the advancing direction of light with the longitudinal direction of the etalons (see for example PLT 1). Such air gap type etalons have to be adjusted in transmitted waveform. In general, this adjustment of transmitted waveform is carried out by adjusting the incidence angle of the light and the temperature.